I find this disturbing. It should be within the power of law enforcement agencies to close down websites that support or promote violence (which is implied here in relation to anti-capitalism protests), but I feel that any such action should only take place after due process in a court of law, with the presumption of innocence until guilt is proven.
Either way, to target the hosting company seems pretty ineffectual – it is easy to find replacement hosting in a matter of minutes, and not too difficult to find hosting that is beyond the reach of the western authorities. I note that the sites concerned are largely online again already.